Effects of pre-analytical sample care and analysis methodology on measures of metabolic acidosis in hemodialysis patients

Introduction

We evaluated the effects of pre-analytical care on total carbon dioxide (tCO₂) in hemodialysis patients, as calculated by blood gas analysis (ctCO₂) or measured by an enzymatic assay (mtCO₂).

Methods

Blood samples were collected via vascular access before dialysis sessions. For blood gas analysis, eight aliquots were collected, refrigerated or non-refrigerated, and analyzed at 0, 4, 8, and 24 h after collection. A blood sample was then collected for the enzymatic method and distributed into 14 aliquots. Half of the aliquots were refrigerated. The samples analyzed at time point 0 were centrifuged immediately. The remaining aliquots of both the refrigerated and non-refrigerated clusters were centrifuged before storage. Samples were analyzed at 4, 8, and 24 h post-collection.

Findings

By blood gas analysis, no significant change was found in bicarbonate values over time, either in the non-refrigerated or refrigerated samples. ctCO₂ values during the experiment showed a minor but statistically significant increase of questionable clinical relevance in both non-refrigerated and refrigerated aliquots. In the enzymatic assay, the reduction in mtCO₂ levels during the experiment was negligible. The median absolute reductions at the end of the experiment were 1.77, 1.21, 1.04, and 1.12 mmol/L for the non-centrifuged/non-refrigerated, centrifuged/non-refrigerated, non-centrifuged/refrigerated, and centrifuged/refrigerated aliquots, respectively.

Discussion

Our results suggest that measured or calculated tCO₂ levels of capped and cooled samples are adequate for analyzing the acid–base status of hemodialysis patients, even when such determination is not performed immediately after collection.